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Origin of peripheral dose contributions
Anders A
.
Patient scatter
– Unavoidable
– Decrease from target essentially as:
n
=1 column shaped scatter source
n
=2 “blob” shaped scatter source
Head scatter
−
Sources are all irradiated parts of the treatment head, main source the flattening filter
−
Limited by the collimating devices
−
Machine design dependent (FFF machines have less!)
e
r
n
r
µ
− ⋅
Leakage, including scatter leakage
−
Depends on collimator and shield thicknesses and material (density)
−
Collimator design dependent
−
Treatment technique dependent
Neutrons
−
Mainly a high Z phenomena at photon energies above photonuclear threshold values
−
Avoidable by lower beam energy
Only one factor user controllable on a daily basis, all other once per decade (replacement)!